1. Field of the Invention
The present invention relates to an effect adder apparatus for an electronic musical instrument and, more particularly, to an apparatus suitably used for adding acoustic effects to an input tone signal.
2. Description of the Prior Art
In a conventional electronic musical instrument, addition of various acoustic effects such as reverberation, chorus, and the like can give profoundness and depth to tones like in acoustic musical instruments, and such effects are important factors in colorful musical expressions. In an electronic musical Instrument which adds acoustic effects by a microprocessor-controlled effect adder circuit controlled by a microprocessor (CPU), various effects are added to the input tone signal by predetermined operations using various coefficients.
Various coefficients used in operations for effect addition are stored in a coefficient memory in the effect adder circuit. Some of these coefficients have fixed values from the very beginning of power ON, but some other coefficients must be updated in accordance with player's panel operations, program, or the like during processing of the tone signal. In such case, if the coefficient to be updated is abruptly changed to a new value, the output signals before and after the change become discontinuous, and click noise is unwantedly produced upon switching.
To prevent such problem, the CPU smoothes the coefficient to be updated, and gradually transfers new coefficient values obtained by smoothing to the coefficient memory in the effect adder circuit. However, this processing imposes a heavy processing load on the CPU, and may delay other processing operations (keyboard processing, panel processing, and the like) that the CPU must perform. Conversely, when the processing load on the CPU is to be reduced, a lower smoothing precision must be inevitably set, resulting in generation of click noises.
In order to solve the above problems, the coefficient is smoothed by using fundamental operation circuits in the effect adder circuit in place of the CPU. However, in this case smoothing wastes hardware resources for implementing effect addition, resulting in deterioration of effect addition quality.